排序方式： 共有274条查询结果，搜索用时 15 毫秒
161.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(47):15245-15248
The total synthesis of lycoricidine and narciclasine is enabled by an arenophile‐mediated dearomative dihydroxylation of bromobenzene. Subsequent transpositive Suzuki coupling and cycloreversion deliver a key biaryl dihydrodiol intermediate, which is rapidly converted into lycoricidine through site‐selective syn ‐1,4‐hydroxyamination and deprotection. The total synthesis of narciclasine is accomplished by the late‐stage, amide‐directed C−H hydroxylation of a lycoricidine intermediate. Moreover, the general applicability of this strategy to access dihydroxylated biphenyls is demonstrated with several examples. 相似文献
162.
163.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(4):1107-1111
Stereoselective total syntheses of (−)‐histrionicotoxin and (−)‐histrionicotoxin 235A are described. The 1‐azaspiro[5.5]undecane skeleton was constructed diastereoselectively by a radical translocation–cyclization reaction involving a chiral cyclic acetal; the use of tris(trimethylsilyl)silane was crucial for the high diastereoselectivity. The cyclization product was converted into (−)‐histrionicotoxin 235A through a one‐pot partial‐reduction–allylation reaction of a derivative containing an unprotected lactam. Finally, two terminal alkenes were transformed into enynes with the 1,3‐amino alcohol protected as an oxathiazolidine oxide to complete the total synthesis of (−)‐histrionicotoxin. 相似文献
164.
165.
《Chemie in Unserer Zeit》2018,52(4):238-248
Quinine, isolated in pure form already in 1820 is a medication that was and is used to treat malaria since centuries. As its source, the cinchona tree, it is a legend and of utmost medical benefit until today. We present excerpts of reviews, which describe the background story of cinchona tree, and quinine as well as of the efforts made for isolation, structure elucidation and total synthesis of this alkaloid. This illustrates how this work forwarded organic chemistry as a whole. A possible personal uptake of quinine as bitter substance is discussed, looking at Tonic Water, Gin Tonic, and their impressive blue fluorescence under UV irradiation. Other uses of quinine in pharmacy and organic synthesis are shown. We describe the isolation of pure quinine from cinchona bark and present its complete set of spectra together with interpretations. Based on a laboratory project this paper is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009). 相似文献
166.
167.
168.
Bo Xu Bingyang Wang Wen Xun Fayang G. Qiu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5810-5813
A concise and highly stereoselective total synthesis of the Daphniphyllum alkaloids (?)‐daphenylline has been accomplished. The synthesis was started from (S)‐carvone and proceeded via a stereoselective Mg(ClO4)2‐catalyzed intramolecular amide addition cyclization, an intramolecular Diels–Alder reaction to construct the ABCD tetracyclic core architecture, and a Robinson annulation coupled with an oxidative aromatization sequence. Finally, the DF ring system was installed through an intramolecular Friedel–Crafts cyclization. The total synthesis of (?)‐daphenylline is achieved in 19 steps in the longest reaction sequence and in 7.6 % overall yield. 相似文献
169.
Meike Sapotta Anja Hofmann David Bialas Frank Würthner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3554-3558
Herein, we report a water‐soluble macrocyclic host based on perylene bisimide (PBI) chromophores that recognizes natural aromatic alkaloids in aqueous media by intercalating them into its hydrophobic cavity. The host–guest binding properties of our newly designed receptor with several alkaloids were studied by UV/Vis and fluorescence titration experiments as the optical properties of the chromophoric host change significantly upon complexation of guests. Structural information on the host–guest complexes was obtained by 1D and 2D NMR spectroscopy and molecular modelling. Our studies reveal a structure–binding property relationship for a series of structurally diverse aromatic alkaloids with the new receptor and higher binding affinity for the class of harmala alkaloids. To our knowledge, this is the first example of a chromophoric macrocyclic host employed as a molecular probe for the recognition of aromatic alkaloids. 相似文献
170.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(31):9190-9194
Hapalindole U ( 4 ) is a validated biosynthetic precursor to ambiguine alkaloids (Angew. Chem. Int. Ed . 2016 , 55 , 5780), of which biogenetic origin remains unknown. The recent discovery of AmbU4 (or FamC1) protein encoded in the ambiguine biosynthetic pathway (J. Am. Chem. Soc . 2015 , 137 , 15366), an isomerocyclase that can rearrange and cyclize geranylated indolenine ( 2 ) to a previously unknown 12‐epi ‐hapalindole U ( 3 ), raised the question whether 3 is a direct precursor to 4 or an artifact arising from the limited in vitro experiments. Here we report a systematic approach that led to the discovery of an unprecedented calcium‐dependent AmbU1‐AmbU4 enzymatic complex for the selective formation of 4 . This discovery refuted the intermediacy of 3 and bridged the missing links in the early‐stage biosynthesis of ambiguines. This work further established the isomerocyclases involved in the biogenesis of hapalindole‐type alkaloids as a new family of calcium‐dependent enzymes, where the metal ions are shown critical for their enzymatic activities and selectivities. 相似文献